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    <title>ShellCheck: SC3054 – In POSIX sh, array references are undefined.</title>
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    <h1>SC3054 – ShellCheck Wiki</h1>
    <a href="https://github.com/koalaman/shellcheck/wiki/SC3054">See this page on GitHub</a>
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    <h2 id="in-posix-sh-array-references-are-undefined">In POSIX sh, array
references are undefined.</h2>
<p>(or "In dash, ... are not supported." when using
<code>dash</code>)</p>
<h3 id="problematic-code">Problematic code:</h3>
<div class="sourceCode" id="cb1"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb1-1"><a href="SC3054.html#cb1-1" aria-hidden="true" tabindex="-1"></a><span class="co">#!/bin/sh</span></span>
<span id="cb1-2"><a href="SC3054.html#cb1-2" aria-hidden="true" tabindex="-1"></a><span class="va">var</span><span class="op">=</span><span class="va">(</span>foo bar<span class="va">)</span></span>
<span id="cb1-3"><a href="SC3054.html#cb1-3" aria-hidden="true" tabindex="-1"></a><span class="bu">echo</span> <span class="st">&quot;</span><span class="va">${var</span><span class="op">[</span><span class="dv">1</span><span class="op">]</span><span class="va">}</span><span class="st">&quot;</span></span></code></pre></div>
<h3 id="correct-code">Correct code:</h3>
<p>The easiest solution is to switch to a shell that does support
arrays, like <code>bash</code>:</p>
<div class="sourceCode" id="cb2"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb2-1"><a href="SC3054.html#cb2-1" aria-hidden="true" tabindex="-1"></a><span class="co">#!/bin/bash</span></span>
<span id="cb2-2"><a href="SC3054.html#cb2-2" aria-hidden="true" tabindex="-1"></a><span class="va">var</span><span class="op">=</span><span class="va">(</span>foo bar<span class="va">)</span></span>
<span id="cb2-3"><a href="SC3054.html#cb2-3" aria-hidden="true" tabindex="-1"></a><span class="bu">echo</span> <span class="st">&quot;</span><span class="va">${var</span><span class="op">[</span><span class="dv">1</span><span class="op">]</span><span class="va">}</span><span class="st">&quot;</span></span></code></pre></div>
<p>Alternatively, rewrite the logic to use e.g. indirect variable
references or <code>set</code>:</p>
<div class="sourceCode" id="cb3"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb3-1"><a href="SC3054.html#cb3-1" aria-hidden="true" tabindex="-1"></a><span class="co">#!/bin/sh</span></span>
<span id="cb3-2"><a href="SC3054.html#cb3-2" aria-hidden="true" tabindex="-1"></a><span class="bu">set</span> <span class="at">--</span> foo bar</span>
<span id="cb3-3"><a href="SC3054.html#cb3-3" aria-hidden="true" tabindex="-1"></a><span class="bu">echo</span> <span class="st">&quot;</span><span class="va">$2</span><span class="st">&quot;</span></span></code></pre></div>
<h3 id="rationale">Rationale:</h3>
<p>Arrays are supported in <code>bash</code> and <code>ksh</code>, but
not in <code>dash</code> or POSIX <code>sh</code>. Either switch to a
shell that supports them, or rewrite your script without relying on
arrays. This may not be straight forward.</p>
<h3 id="exceptions">Exceptions:</h3>
<p>If you only intend to target shells that supports this feature, you
can change the shebang to a shell that guarantees support, or <a
href="ignore.html">ignore</a> this warning.</p>
<p>You can use <code># shellcheck disable=SC3000-SC4000</code> to ignore
all such compatibility warnings.</p>
<h3 id="related-resources">Related resources:</h3>
<ul>
<li>Help by adding links to BashFAQ, StackOverflow, man pages, POSIX,
etc!</li>
</ul>
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